There was a car in front of me that was making weird movements, so it was scary.
The car that was running before mine was moving about in a strange way, so I was scared.
ご質問ありがとうございます。
① "There was a car in front of me that was making weird movements,"＝「私の前にいた車は変な動作をしていた、」
"so it was scary."＝「なので怖かった。」
② "The car that was running before mine was moving about in a strange way,"＝「私の前に走っている車は変な動きをしていた、」
"so I was scared."＝「なので、私は怖かった。」
ご参考までに。
A car in front of me was swerving all over the road. It was scary.
この場合、次のような言い方ができますよ。
ーA car in front of me was swerving all over the road. It was scary.
「前の車が道路からあちこちそれて走っていて、怖かった」
to swerve で「（まっすぐな進路から）それる」
ご参考まで！
アメリカ合衆国 
カナダ 
